Closed loop control techniques for displacement sensors with optical readout

A system for controlling displacement sensors with optical readout, comprising:

• a housing;
• a proof mass configured to move within the housing;
• a light source disposed within the housing;
• a detector disposed within the housing that detects light from the light source and generates, based on the light, an optical signal indicative of a relative displacement between the proof mass and the housing;
• an electromagnetic device configured to influence the relative motion between the housing and the proof mass;
• and
• a control system configured to:
• identify a period of the optical signal;
• identify a plurality of fringes of the optical signal;
• provide a signal to the electromagnetic device to lock the relative displacement between the proof mass and the housing to a range corresponding to a single fringe of the plurality of fringes of the optical signal;
• suspend closed loop control for a period of time to change a fringe to which the control system is locked;
• and
• resume, upon completion of the period of time, closed loop control to lock to the single fringe.

A system for detecting seismic activity, comprising:

• a seismic sensor comprising:
• a housing;
• a proof mass configured to move within the housing responsive to seismic activity;
• a light source disposed within the housing;
• a detector disposed within the housing that detects light from the light source and generates, based on the light, an optical signal indicative of a relative displacement between the proof mass and the housing;
• an electromagnetic device configured to influence the relative motion between the housing and the proof mass;
• and
• a control system configured to:
• identify a period of the optical signal;
• identify a plurality of fringes of the optical signal;
• provide a signal to the electromagnetic device to lock the relative displacement between the proof mass and the housing to a range corresponding to a first fringe of the plurality of fringes of the optical signal, wherein the seismic sensor detects seismic motion based at least in part on measuring the relative displacement of the proof mass and the housing;
• and
• apply a signal to the electromagnetic device to change a first state locked to the first fringe to a second state locked to a second fringe of the plurality of fringes, and wherein the second fringe corresponds to a position closer to mechanical zero of the proof mass and housing system than the first fringe.